With fast development of communications technologies, xDSL (digital subscriber line) as a high-speed data transmission technology is widely applied. However, G.fast (gigabit DSL) as a latest xDSL technology uses a high frequency band during data transmission, and therefore a crosstalk phenomenon is very severe. To eliminate an effect of crosstalk on data transmission, a vectoring technology emerges as the times require.
In a vectoring system shown in FIG. 1, when downlink transmission is performed, each transceiver of a sending party serves as a sending end, each transceiver of a receiving party serves as a receive end, and before undergoing IFFT (Inverse Fast Fourier Transform) transformation, a transmit signal of each transceiver of the sending party needs to be precoded by a canceller (Precoder). After being precoded and undergoing the IFFT transformation, the transmit signal may be sent. A downlink canceller used for crosstalk cancellation is located before a module that sends data, and therefore the downlink canceller is also referred to as a downlink precoder, and a downlink cancellation matrix is also referred to as a downlink precoding matrix. Therefore, a meaning of the downlink canceller is the same as that of the downlink precoder, and a meaning of the downlink cancellation matrix is the same as that of the downlink precoding matrix. During data transmission, to prevent transmission of the transmit signal from generating excessively large interference to another signal, power of the transmit signal is generally controlled.
In the prior art, two power control manners are generally included. In a first control manner, after performing inversion according to a channel matrix to obtain a cancellation matrix, a VCE (vectoring control entity) obtains a diagonal matrix according to the cancellation matrix, and sends the obtained diagonal matrix to a transceiver; and the transceiver calculates, according to the value of a corresponding diagonal element of the diagonal matrix, a power control factor that is less than or equal to the corresponding diagonal element of the diagonal matrix, and then multiplies the power control factor by a transmit signal before cancellation, to obtain a transmit signal whose power is scaled, thereby implementing control of power of the transmit signal. In a second control manner, after performing inversion according to a channel matrix to obtain a cancellation matrix, a VCE obtains a diagonal matrix according to the cancellation matrix, uses a matrix obtained after the cancellation matrix is multiplied by the diagonal matrix as a new cancellation matrix, and sends the new cancellation matrix to a canceller; and the canceller encodes a transmit signal according to the new cancellation matrix, thereby implementing control of power of the transmit signal.
During implementation of the present invention, the inventor finds that the prior art at least has the following problem:
No matter whether the first control manner or the second control manner is used, inversion needs to be performed according to a channel matrix to calculate a cancellation matrix, each element value of a cancellation matrix obtained after inversion is performed on a channel matrix whose condition number is bad is excessively large, and each element value of a diagonal matrix is excessively small, and therefore an extent to which power of a transmit signal is scaled is excessively large, which alleviates strength of the narrowed transmit signal, so that a sending rate is greatly affected, which severely reduces power use efficiency.